The Klingon homeworld remained canonically unnamed until Star Trek VI: The Undiscovered Country, in which it was identified as "Kronos", spelled that way in the film's script. The spelling "Kronos" was also used in most of the scripts of Star Trek: Deep Space Nine episodes. It was also used in the script of the Star Trek: Enterprise episode "Broken Bow". According to the pronunciation guide in the script of DS9: "Tears of the Prophets", KRO-nos is the phonetic spelling of "Kronos".

"Chronos" was a more rare alternative spelling used in the scripts of only two Star Trek: Deep Space Nine episodes, "Once More Unto the Breach" and "Extreme Measures" The spelling "Kronos" was however identified as the correct one, when it was seen on screen in Star Trek Into Darkness.

That was a fan thing or a book thing. In Star Trek VI there is some talk about a possible evacuation of the Klingon homeworld but it was never mentioned again. In TNG some parts of the capital are supposed to be very old so it doesn't seem likely it's a newly settled planet.

We saw that a fragmented moon had impacted Kronos. With that in mind, it looked to me like the surface had been devastated. Maybe the mining accident from Star Trek VI came early in this timeline and the empire is in a bit of trouble.